1. Field of the Invention
This invention relates to devices and systems to facilitate replacing wheels and blades, e.g., on a fan, on a rotary element and, more particularly, to split wheel assemblies, e.g., a fan wheel assembly, and split shroud assemblies for use on a high-speed attrition-type coal pulverizer.
2. Background of the Related Art
In coal-fired furnaces, for purposes of improved and more efficient ignition, it is preferred to pulverize the coal to a fine powder before introducing it into the furnace for combustion. Coal pulverization involves systematically comminuting coal to a desired, preferably optimum size, e.g., a fine powder, prior to introduction into a coal-fired furnace. Currently, coal pulverization systems include ball-tube-type mills, vertical roller-type mills, and high-speed, attrition-type pulverizers.
Ball-tube-type mills are low speed mills that have their origins in the 1930's and 1940's. The ball-tube-type mill comprises a plurality of hardened steel balls that are disposed in a large, rotatable barrel. While the barrel rotates, coal is introduced into the barrel. Through the rotating action of the barrel, the steel balls fall onto the coal, pulverizing the coal by the impact. The pulverized coal is then removed and fed into a coal-fired furnace. Ball-tube-type mills are successfully used in conjunction with highly abrasive coal. However, they are relatively slow.
Vertical roller-type mills pulverize coal on a rotating grinding table. A plurality of rollers applies a shearing force and a grinding pressure to the coal hydraulically. The pulverized coal is then removed from the mill using a high velocity stream of air and fed into a coal-fired furnace. Although faster than ball-tube-type mills, vertical roller-type mills are only medium speed mills.
Referring to FIG. 1, a high-speed attrition-type pulverizer 10, e.g., an ATRITA®-type pulverizer, will be described. High-speed attrition-type pulverizers provide three-stages of pulverization, in which each stage is powered by a common rotary assembly 12. Essentially, coal enters the first (crushing) section 2 where a plurality of rotating and reciprocating swing hammers 4 crush the coal against a grid 6. The grid deters passage of coal that has not been crushed sufficiently to a preferred nominal size, e.g., about ¼ in. Once the coal has been reduced to a nominal size, it passes through the grid 6 and, subsequently, is introduced into a second (pulverizing) section 8.
The pulverizing section 8 comprises a rotating impeller 14 that divides the section 8 into interconnected upstream portions 1 and downstream portions 3. In the upstream portion 1 of the pulverizing section 8, the rotating impeller 14 causes the coal from the crushing section 2 to rub together, which further reduces the coal size by attrition. Once the coal has reached a desired nominal dimension, it enters the downstream portion 3 of the pulverizing section 8. In the downstream portion 3, the coal is pulverized between a plurality of pegs 7 moving with the impeller 14 at a high speed of rotation and a plurality of stationary pegs 9. The coal is caught between the stationary pegs 9 and further pulverized when the moving pegs 7 pass between the stationary pegs 9.
When the coal in the downstream portion 3 of the pulverizing section 8 is sufficiently pulverized, it exits the pulverizing section 8 through a rejector assembly. On the other side of the rejector assembly, is a third (exhaust) section 13, which transports the fine, pulverized coal in a fluid stream to the coal-fired furnace (not shown). Typically, the exhaust section 13 comprises a rotating fan wheel 15 having a plurality of fan blades 17. A shroud (not shown) can be added to confine the pulverized coal in the exhaust section 13.
Typically, each of the sections of the high-speed, attrition-type pulverizers 10, i.e., the crushing section 2, the pulverizing section 8, and the exhaust section 13, is structured and arranged to be powered by a shared, or common, rotating shaft 12. Further, in many applications, a plurality of high-speed, attrition-type pulverizers 10 is powered by a shared, or common, rotating shaft 12. For example, it is quite common that a twin pulverizer assembly includes two pulverizers 10 in series, where the exhaust section 13 of one pulverizer 10 can be adjacent to the crushing section 2 of the other pulverizer 10 or the exhaust section 13 of one pulverizer 10 can be adjacent to the exhaust section 13 of the other pulverizer 10 or the crushing section 2 of one pulverizer 10 can be adjacent to the crushing section 2 of the other pulverizer 10.
Regardless of the relative arrangement of each pulverizer 10 in a twin pulverizer assembly or, alternatively, whether there is one or more than one pulverizer 10 on a single rotary shaft 12, periodic maintenance and as-needed repair of the fan wheel assembly 15 requires major disassembly of all sections or some portions of one or more pulverizers 10, which is labor- and time-intensive. Accordingly, it would be desirable to provide a pulverizer in which repair of the fan wheel can be performed without labor- and time-intensive disassembly of major portions of the pulverizer.